Method of treatment of metal surfaces

ABSTRACT

A hard and wear-resistant coating is imparted to a finished article of copper or copper base alloy, by electro-depositing on the surface of the finished article a layer 8-15 microns thick of an alloy which is tin containing 5-10 percent by weight of antimony, and then heating the coated article to diffuse the base and coating metals into each other. The alloying metals with the copper of the substrate may be a minor proportion of at least one of tin 5-15 percent, zinc 15-40 percent, aluminum 6-15 percent, lead 2-18 percent, nickel 12-18 percent, beryllium 0.5-2 percent and iron 0.5-5 percent. Electrodeposition is conducted from a bath having an antimony:tin ionic ratio of 1.7:1 to 1.9:1, a pH of 2.5 to 2.8, and a cathodic current density of 2-8 A/dm2. In the case of a substrate in which the alloying metal is tin or lead, the subsequent heating is 3 hours at 200*C, 2 hours at 300*C and 1 hour at 400*C, followed by slow cooling. If the alloying metal for the copper substrate is zinc, aluminum, nickel and/or beryllium, subsequent heating is 3 hours at 200*C, 2 hours at 300*C, 1 hour at 400*C and 1 hour at 450*C, followed by slow cooling.

United States Patent [191 Polti METHOD OF TREATMENT OF METAL SURFACES [76] Inventor: Jean-Loup Polti, LePetit Pont,

42450 Suryle Comtal, France [22] Filed: Mar. 12, 1974 [21] Appl. No.: 450,282

Related US. Application Data [63] Continuation-in-part of Ser. No. 279,798, Aug. 10, 1972, abandoned, which is a continuation-in-part of Ser. No. 15,871, March 2, 1970, abandoned.

[30] Foreign Application Priority Data 2,458,827 1/1949 Booe 204/43 S 2,825,683 3/1958 Lowenheim et al. 204/43 S 3,074,154 l/l963 Pearson et al 204/37 T X FOREIGN PATENTS OR APPLICATIONS 526,037 9/1940 United Kingdom 204/37 T OTHER PUBLICATIONS A. Brenner, The Electrodeposition of Alloys, Aca- July 1,1975

demic Press, New York, (1963), P- 547-555, (Vol. 2).

Primary Examiner-H0ward S. Williams Assistant Examiner-Aaron Weisstuch Attorney, Agent, or F irm-Young & Thompson [5 7] ABSTRACT A hard and wear-resistant coating is imparted to a finished article of copper or copper base alloy, by electro-depositing on the surface of the finished article a layer 8-15 microns thick of an alloy which is tin containing 5-10 percent by weight of antimony, and then heating the coated article to diffuse the base and coating metals into each other. The alloying metals with the copper of the substrate may be a minor proportion of at least one of tin 5-15 percent, zinc 15-40 percent, aluminum 6-15 percent, lead 2-18 percent, nickel 12-18 percent, beryllium 0.5-2 percent and iron 0.5-5 percent. Electrodeposition is conducted from a bath having an antimonyztin ionic ratio of 1.7:1 to 19:1, a pH of 2.5 to 2.8, and a cathodic current density of 2-8 A/dm In the case of a substrate in which the alloying metal is tin or lead, the subsequent heating is 3 hours at 200C, 2 hours at 300C and 1 hour at 400C, followed by slow cooling. If the alloying metal for the copper substrate is zinc, aluminum, nickel and/or beryllium, subsequent heating is 3 hours at 200C, 2 hours at 300C, 1 hour at 400C and 1 hour at 450C, followed by slow cooling.

5 Claims, N0 Drawings METHOD OF TREATMENT OF METAL SURFACES This application is a continuation-in-part of copending application Ser. No. 297,798, filed Aug. 10, 1972, and now abandoned, which in turn was a continuationin-part of application Ser. No. 15,871, filed Mar. 2, 1970 and now abandoned.

The present invention relates to the surface treatment of finished articles of copper or copper-base alloy, and has for its object the provision of superficial surface layers on such finished articles, which will impart to the articles good sliding frictional properties with resistance to seizure, high wear resistance, high hardness, and good corrosion resistance.

In general, the metals of the substrate or finished article which the process of the present invention is applicable are pure copper, for example for electrical uses; alloys of copper principally with tin, as in the case of bronzes used for general mechanical applications; alloys of copper principally with zinc, that is, brasses, for mechanical uses such as in valves; alloys of copper principally with aluminum, for anticorrosive and particularly maritime uses; and alloys of copper with various other metals such as lead, nickel, beryllium and iron. More particularly, the metals of the substrate may be copper or copper alloyed with a minor proportion in total of at least one member selected from the group consisting of, in weight percentages, 5-15 percent tin, 15-40 percent zinc, 6-15 percent aluminum, 2-18 percent lead, 12-18 percent nickel, 0.5-2 percent beryllium, and 0.5-5 percent iron. In other words, more than one such non-copper metal may be alloyed with copper, but the copper will in any case be 50-100 percent by weight.

The surface of the finished article is prepared for treatment, in the case of most of the substrates such as those whose alloying metal is tin or zinc, by conventional procedures, such as degreasing in a conventional bath of soda, sodium cyanide, sodium carbonate, trisodium phosphate and sodium alkylarlysulphonate, followed by rinsing and depassivation in aqueous 10 percent sulphuric acid. If the alloying metal is principally aluminum, then degreasing and rinsing is conducted as above but the finished article is electrolytically polished in a bath of pure phosphoric acid. These preparatory techniques are conventional and need not be described in greater detail.

Then the article is electroplated with a coating 8-15 microns thick of a tin-antimony alloy containing 510 percent by weight antimony, balance essentially tin. The electroplating bath preferably has a pH between 2.5 and 2.8. Electroplating may be conducted at ambient temperature, e.g., 20C. The bath is preferably agitated, and agitation may be combined with filtration in a conventional manner. The ratio of antimony to tin ions in the plating bath is preferably between about 1.7:1 and 1.9:1. The cathodic current density is preferably about 2 to about 8 amperes per square decimeter. Electrodeposition proceeds at a rate of about 1 to 2 microns of coating thickness per minute, and a brilliant coating is obtained. The thickness of the deposited coating, within the range of 8 to microns, is preferably 8 to 12 microns for alloys of copper with tin and/or zinc, and 10 to 15 microns for alloys of copper with aluminum. The electroplating bath is aqueous and may for example have the following composition:

SnCl 8 to 22 g/l Sb 0 g/l Ammonium citrate -135 g/l Hydrochloric acid 78-85 ml/l Gelatin 2 g/l Salicylic acid 4 g/l Following electrodeposition of the tin-antimony alloy layer, the substrate and coating are diffused into each other by heat treatment. Heat treatment may be conducted in conventional equipment, in ambient air or in a protective atmosphere such as nitrogen, and in the case of copper alloys containing principally tin or lead as the alloying constituent, is conducted for about 3 hours at about 200C, about 2 hours at about 300C and about 1 hour at about 400C,'followed by slow cooling, that is, cooling in the ambient air. In the case of copper alloys whose alloying metal is zinc, aluminum, nickel or beryllium, the same heat treatment is followed by 1 hour at 450C, and then slow cooling.

In the case of copper and copper-tin alloys, the superficial layer after heat treatment has a thickness between 10 and 15 microns, a hardness between 400 and 500 Vickers 15 (that is, measured under-a load of 15 grams), and consists essentially of the two phases 6 and 8 with e predominating at the exposed surface and 3 predominating at the interface, with reference to the equilibrium phase diagram, with traces of antimony throughout. The superficial layer thus is essentially two-phase.

In the case of copper-zinc alloys, the superficial layer after heat treatment will have a thickness of 10-15 microns, a hardness of about 550-650 Vickers 15, and will be a single phase layer of copper-zinc-tin-antimony alloy.

In the case of copper-aluminum alloys, the superficial layer after heat treatment will have a thickness of 15-30 microns, a hardness of 780-880 Vickers 15 and will be in the form of strata of a phase rich in copper and tin and poor in antimony and aluminum, and B phase rich in copper and aluminum and poor in tin and antimony.

To enable those having ordinary skill in this field to practice the invention, the following illustrative but non-limitative examples are given:

Example 1 A bronze gear containing 12 percent tin, a trace of phosphorus, balance essentially copper, is subjected to conventional degreasing in an aqueous solution of soda, sodium cyanide, sodium carbonate, trisodium phosphate and sodium arylalkylsulphonate, rinsing and depassivation in aqueous 10 percent sulphuric acid. It is then electroplated in an aqueous electroplating solution containing 20 g/l SnCl 2, 32 g/l of Sb O g/l of ammonium citrate, 80 ml/l of hydrochloric acid, 2 g/l of gelatin and 4 g/l of salicylic acid, having a pH of 2.6, and a temperature of 20C, with agitation, at a cathodic current density of 5A/dm for 6 minutes, until a brilliant layer of tin alloy containing 7 percent antimony, balance essentially tin, is deposited thereon to a thickness of 10 microns. The plated article is then heated for 3 hours at 200C, 2 hours at 300C and 1 hour at 400C, in ambient air, after which heatiag is discontinued and the article slowly cools in aif at 20C:

The superficial layer after heat treatment has a thickness of microns and an average hardness of 480 Vickers l5. The gear is then run in contact with a steel worm for thirteen months of regular use but no substantial wear is noted at the end of that time. For comparison purposes, a same gear which has not been treated as above is run under the same conditions in contact with a same steel worm; and after three months of regular usage the untreated gear is so worn as to be unusable.

Example 2 The cylinder of a high pressure oil pump for lubricant distribution has a composition of 39 percent zinc, 2 percent lead, balance essentially copper. It is treated as in Example 1, except that during the heat treatment, after the heating at 400C and before the slow cooling, it is heated for 1 hour at 450C. After heat treatment, the superficial layer has a thickness of 15 microns and a hardness of 650 Vickers 15. It is run in frictional contact with a steel piston for 5,000 hours and the pump is disassembled and examined and the brass cylinder is found to have no appreciable wear on its frictional surface. For purposes of comparison, the same cylinder which has not been given the above treatment is run in contact with a same piston and seizes after several hundred operations, that is, after substantially less operation than was successfully withstood by the treated cylinder.

Example 3 A finished article comprising a journal bearing for the rolls of a metal rolling mill has the composition 9 percent aluminum, 4 percent nickel, 2.5 percent iron, balance essentially copper. It is subjected to the treatment of Example 1, except that the preparation for i electroplating includes the step of electrolytic polishing in a phosphoric acid bath instead of depassivation in sulphuric acid solution. Also, electrodeposition is conducted for 9 minutes until the deposited coating has a thickness of 15 microns. Heat treatment is as in Example 2. The thickness of the superficial layer after heat treatment is microns and this layer has a hardness of 850 Vickers 15. The treated journal bearing is placed inregular use in a rolling mill for 2 /2 years and undergoes some wear but not enough to take it out of service. By contrast, a same journal bearing which has not been subjected to the above treatment is subjected to the same usage and after 2% months is very severely worn, more so even than the treated journal bearing after 2% years.-

From a consideration of the foregoing disclosure, therefore, it will be evident that the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit of the invention, as those skilled in this art will readily understand. Such modifications and variations are considered to be within the purview and .scope of the present invention as defined by the appended claims.

Having described my invention, I claim:

1. A method of forming a hard and wearresistant coating on a finished article made of a copper-based alloy, comprising electrodepositing on the surface of a said article a layer 8-15 microns thick of an alloy consisting essentially of' tin containing 5-10 percent 'by weight antimony, said electrodeposition being conducted in an aqueous bath having a pH of about 2.5 to about 2.8, having a proportion of antimony ions to tin ions in the range from about 1.7:1 to 1.9: l and having a cathodic current density of about 2 to about 8 amperes per square decimeter, and then heating said article to diffuse the metals of'said layer and surface into each other.

' 2. A method as claimed in claim 1, in which said bath contains about 18 to about 22 grams per liter of SnCl about 30 to about 34 grams per liter of Sb 0 about to about grams per liter of ammonium citrate, about 78 to about 85 milliliters per liter of hydrochloric acid, about 2 grams per liter of gelatin and about 4 grams per liter of salicylic acid.

3. A method as claimed in claim 1, the metal of said article consisting essentially of at least one member selected from the group consisting in weight percentages of 5-15 percent tin, 15-40 percent zinc, 6l5 percent aluminum, 2-18 percent lead, 12-18 percent nickel, 0.5-2 percent beryllium, 0.5-5 percent iron, and at least 50 percent copper.

4. A method as claimed in claim 3, in which said at least one member is selected from the group consisting of tin and lead and said heating is conducted for about 3 hours at about 200C, then for about 2 hours at about 300C, and then for about 1 hour at about 400C, fol lowed by slow cooling. I

5. A method as claimed in claim 3, in which said at least one member is selected from the group consisting of zinc, aluminum, nickel and beryllium, and said heating is conducted for about 3 hours at about 200C, then for about 2 hours at about 300C, then for about 1 hour at about 400C, and then for about 1 hour at about 450C, followed by slow cooling. 

1. A METHOD OF FORMING A HARD AND WEAR-RESISTANT COATING ON A FINISHED ARTICLE MADE OF A COPPER-BASED ALLOY, COMPRISING ELECTRODEPOSITING ON THE SURFACE OF A SAID ARTICLE A LAYER 8-15 MICRONS THICK OF AN ALLOY CONSISTING ESSENTIALLY OF TIN CONTAINING 5-10 PERCENT BY WEIGHT ANTIMONY, SAID ELECTRODEPOSITION BEING CONDUCTED IN AN AQUEOUS BATH HAVING A PH OF ABOUT 2.5 TO ABOUT 2.8, HAVING A PROPORTION OF ANTIMONY IONS TO TIN IONS IN THE RANGE FROM ABOUT 1.7:1 TO 1.9:1, AND HAVING A CATHODIC CURRENT DENSITY OF ABOUT 2 TO ABOUT 8 AMPERES PER SQUARE DECIMETER, AND THEN HEATING SAID ARTICLE TO DIFFUSE THE METALS OF SAID LAYER AND SURFACE INTO EACH OTHER.
 2. A METHOD AS CLAIMED IN CLAIM 1, IN WHICH SAID SAID BATH CONTAINS ABOUT 18 TO ABOUT 22 GRAMS PER LITER OF SNCL2, ABOUT 30 TO ABOUT 34 GRAMS PER LITER OF SB2O3, ABOUT 125 TO ABOUT 135 GRAMS PER LITER OF AMMONIUM CITRATE, ABOUT 78 TO ABOUT 85 MILLILITERS PER LITER OF HYDROCHLORIC ACID, ABOUT 2 GRAMS PER LITER OF GELATIN AND ABOUT 4 GRAMS PER LITER OF SALICYCLIC ACID.
 3. A method as claimed in claim 1, the metal of said article consisting essentially of at least one member selected from the group consisting in weight percentages of 5-15 percent tin, 15-40 percent zinc, 6-15 percent aluminum, 2-18 percent lead, 12-18 percent nickel, 0.5-2 percent beryllium, 0.5-5 percent iron, and at least 50 percent copper.
 4. A method as claimed in claim 3, in which said at least one member is selected from the group consisting of tin and lead and said heating is conducted for about 3 hours at about 200*C, then for about 2 hours at about 300*C, and then for about 1 hour at about 400*C, followed by slow cooling.
 5. A method as claimed in claim 3, in which said at least one member is selected from the group consisting of zinc, aluminum, nickel and beryllium, and said heating is conducted for about 3 hours at about 200*C, then for about 2 hours at about 300*C, then for about 1 hour at about 400*C, and then for about 1 hour at about 450*C, followed by slow cooling. 